The present invention relates to communications and, more specifically, to measuring channel characteristics in a high-speed serial channel.
A SerDes or serializer/deserializer is an integrated circuit (IC or chip) transceiver that converts parallel data to serial data and vice-versa. The transmitter section (Tx) is a parallel-to-serial converter, and the receiver section (Rx) is a serial-to-serial converter. Multiple SerDes interfaces are often housed in a single package. SerDes chips facilitate the transmission of parallel data between two points over serial streams, reducing the number of data paths and thus the number of connecting PINs or wires required.
The Tx block typically has a parallel clock input, a set of data input lines, and input data latches. It may use an external Phase-locked loop (PLL) to multiply the incoming parallel clock up to the serial frequency. The simplest form of the Tx block has a single shift register that receives the parallel data once per parallel clock, and shifts it out at the higher serial clock rate.
The Rx block typically has a receive clock output, a set of data output lines, and output data latches. The receive clock may have been recovered from the data by the serial clock recovery technique. The Rx block then divides the incoming clock down to the parallel rate. Implementations typically have two registers connected as a double buffer. One register is used to clock in the serial stream, and the other is used to hold the data for the slower, parallel side.
The ability to determine the signal integrity of data acquired over a high speed SerDes (HSS), such as eye quality and insertion loss, after having been equalized by the receiver has been an illusive task in the HSS design realm. The information contained in such data allows for the characterization of the receive side amplifying and equalization circuitry. Past techniques to attain such information have involved the use of a combination of lab measurements and simulation since direct measurement of an on-chip circuit node was impossible.